Circuit comprising an arc-discharge tube



Feb. 28, 1956 E. MANN 2,736,842

INVENTOR Ernb Mann y Agent CIRCUIT COMPRISING rligN ARC-DISCHARGE TUBErnti Mann, Eindhoven, Netherlands, assignor to Hartford National Bankand Trust Company, Hartford, Comm, as trustee Application'March 7,1952,'Serial No. 275,419

( Ilaims priority, application Netherlands April 17, 1951 3 Claims. (Cl.315-263) This invention relates to a starting arrangement for igniting alow-pressure arc discharge tube. In particular, the invention relates toa starting arrangement for a tube of that type employing an auxiliarystarting electrode.

The main object of the invention is to reduce the potential necessaryfor igniting a tube of the foregoing type.

This and other objects of the invention will be best understood from thefollowing description thereof.

According to the invention, the main electrodes and the auxiliaryelectrode of a low-pressure arc discharge tube are connected in serieswith an inductor serving to limit current flow through the tube. Inorder to decrease the igniting voltage of said tube an auxiliaryimpedance is arranged in parallel with the inductor and is connectedacross the inductor by means of a relay which is operative above onlyduring the starting cycle of the tube.

In the preferred arrangement, the auxiliary impedance is connected inparallel with the inductor through a magnetic relay whose contacts arenormally closed until the relay is energized by current flowing throughits winding.

In this arrangement the energizing coil is arranged to open the relaywhen the tube current exceeds 0.7 times the normal operating current ofthe tube thereby removing the auxiliary impedance from the circuit.

The value of the auxiliary impedance should be preferably less thanabout 0.2 times the impedance of the inductor during normal operatingcurrent in the tube, and more preferably, between about 0.05 and 0.1times the impedance of the inductor.

The invention will now be described with reference to the accompanyingdrawing in which the sole figure shows one form of starting arrangementexemplifying the invention.

Referring to the figure, a low-pressure arc-discharge tube 1 comprises apair of activated main electrodes 7, 8 and an auxiliary electrode 9connected to one of the main electrodes 8 and extending therefromtowards the other main electrode 7. The tube 1 is connected through aseries inductor 2 and a switch 3 to terminals 4, 5 of a suitable sourceof potential.

A resistor 10, connected in series with a magnetic relay 11, isconnected in parallel with the inductor. The energizing coil 12 for therelay 11 is connected in series with the tube. The relay 11 is normallyclosed when deenergized.

The following specific example will illustrate the invention.

The tube 1 in the drawing is filled with argon and also contains a smallquantity of mercury designated by a droplet 6.

The tube is approximately 120 cms. long and has an internal diameter ofabout mms. and has main electrodes 7, 8 which are activated withconventional materials, for example strontium and barium compounds. Theauxiliary electrode 9 comprises a strip having a width of about 3 mms.and extends substantially throughout the length of the tube along aninner wall thereof, and consists of a mixture of graphite and enamelwith an overall resistance of approximately 2000 ohms.

The inductor 2 has an impedance of about 400 ohms at normal operatingcurrent while the resistor 10 has an impedance of about 30 ohms at acurrent of 25-100 milliamperes. The relay 11 is arranged to open when acurrent of 300 to 350 milliamperes flows through the energizing coil 12.

With an alternating voltage of 220 volts across terminals 4 and 5 andswitch 3 closed, a glow discharge is struck between the main electrode 7as a cathode and the auxiliary electrode 9 as an anode. The glowdischarge thus developed creeps along the auxiliary electrode 9 until itultimately reaches the other main electrode 8 which results in a currentflow of about 25 to ma. The main electrodes 7, 8 are heated by the glowdischarge until the emission temperature of the active compounds isreached, at which time the glow discharge changes into an arc-discharge,which should occur within half a second after the application of thevoltage and results in a current flow of about 250 ma. and finally asteady state arc-discharge current of about 420 ma.

Upon closing the switch, resistor 10 is shunted across the inductor 2thus greatly reducing the impedance of the combination, thereby allowinga higher voltage to appear across the tube terminals. When the glowdischarge has changed into an arc-discharge, the current flowing throughthe tube 1 rapidly increases. Upon reaching the value of 300 ma, therelay 11 becomes energized thereby breaking the circuit between theresistor 10 and the inductor 2 and permitting the inductor 2 to controlthe steady state operating current within the circuit. It has been foundthat the tube described above has ignited with a supply voltage as lowas 200 volts within half-a-second.

The magnetic relay 11 has the further advantage that upon aninterruption of the supply potential, the relay 11 is de-energized andthe resistor 10 immediately reconnected in parallel with the inductor 2,so that the tube will automatically reignite if the supply potential isonce more impressed across the circuit.

While the invention has been described in connection with specificexamples and in specific applications, other modifications thereof willbe readily apparent to those skilled in the art without departing fromthe invention as defined in the appended claims.

What I claim is:

l. A circuit arrangement comprising a low-pressure arc-discharge tubehaving a given operating voltage and adapted to conduct a given value ofcurrent upon reaching the arc-discharge condition, said tube including apair of activated main electrodes and an auxiliary electrode 7 connectedto one of the main electrodes and extending therefrom towards the othermain electrode for igniting the tube Without preheating the mainelectrodes, a potential source having a voltage greater than saidoperating voltage, and inductor having a given value of inductanceconnected in series with the tube and said source, an auxiliaryimpedance shunting said inductor, and a relay in series with said tubeand responsive to the discharge current flowing through said tube todisconnect said auxiliary impedance from the circuit immediately afterthe discharge current through said tube has achieved a predeterminedvalue.

2. A circuit arrangement comprising a low-pressure arc-discharge tubehaving a given operating voltage and adapted to conduct a given value ofcurrent upon reaching the arc-discharge condition, said tube including apair of activated main electrodes and an auxiliary electrode connectedto one of the main electrodes and extending therefrom towards the othermain electrode for igniting the tube without preheating the mainelectrodes, a potential source having a voltage greater than saidoperating voltage, an inductor having a given value of inductanceconnected in series with the tube and said source, an auxiliaryimpedance shunting said inductor and having a value lower than about 0.2times the impedance of said inductor at the given value of current, anda relay in series with said tube and responsive to the discharge currentflowing through said tube to disconnect said auxiliary irnpedance fromthe circuit immediately after the discharge current through said tubeexceeds 0.7 times said given current.

3. A circuit arrangement comprising a low-pressure arcdischarge tubehaving a given operating voltage and adapted to conduct a given value ofcurrent upon reaching the arc-discharge condition, said tube including apair of activated main electrodes and an auxiliary electrode connectedto one of the main electrodes and extending therefrom towards the othermain electrode for igniting the tube without preheating the mainelectrodes, a potential source having a voltage greater than saidoperating voltage, and inductor having a given value of inductance 4connected in series with the tube and said source, a re-. sistorshunting said inductor and having a value between about 0.05 and 0.1times the impedance of said inductor at the given value of current, anda relay in series with said tube and responsive to the discharge currentflowing through said tube to disconnect said resistor from the circuitimmediately after the discharge current through said tube exceeds 0.7times said given current.

References Cited in the file of this patent UNITED STATES PATENTS TowerMar. 25, 1919 2,094,647 Freitag Oct. 5, 1937 2,182,609 Bethenod Dec.5',- 1939 2,266,616 Scott Dec. 16, 1941 2,462,336 Ruff Feb. 22, 19492,485,398 Mandi Oct. 18, 1949 2,491,854 Force Dec. 20, 1949

